During operation of a direct-injection Otto-cycle engine, injection nozzles inject fuel into one or more combustion chambers to achieve a desired air/fuel ratio (e.g., stoichiometric mixture). However, coking or carbon deposition, may occur on the fuel injectors, leading to a narrowing of the fuel injector orifices. Specifically, carbonaceous deposits may form on a closing body and/or on a valve seat of an injection valve. The deposits can partially and in some examples, completely block the orifices of the fuel injectors, reducing an amount of fuel that is injected into the combustion chambers. This in turn can lead to increased particle emissions of the Otto-cycle engine.
Some example approaches aimed at reducing injector coking include injecting an agent that dissolves the coking deposits. For example, DE 101 17 507 A1 discloses a method for, during operation of the Otto-cycle engine, injecting a coke-dissolving agent into an intake duct of the Otto-cycle engine.
However, the inventors of the present application have recognized problems with the above approaches. For example, coking of injection nozzles of an Otto-cycle engine may occur more intensely if the Otto-cycle engine is often operated in a part-load range. At high loads and at full load, deposits on the injection valves are partially burned off or are partially spalled from the injection valves owing to thermal effects. However, if the engine is continually operated in a part-load range, coking deposits may accumulate and increase emissions, and reduce engine performance. In another example, the coke-dissolving agent may also be used as a knock control fluid, and may be injected into the engine cylinders to reduce and/or prevent engine knock. However, the inventors herein have recognized that the coke-dissolving agent may become depleted with frequent injections into the intake, and thus may not be available when needed for engine knock control/prevention.
The inventors herein have devised systems and methods for addressing the issues described above. In one example, the issues described above may be addressed by a system for removing coking deposits from at least one injection nozzle of an Otto-cycle engine, the at least one injection nozzle configured to inject fuel directly into a combustion chamber of the Otto-cycle engine, where the Otto-cycle engine receives intake air via at least one intake unit which serves exclusively for conducting intake air, and where the at least one intake unit includes a humidification unit, which when activated, humidifies intake air flowing through the at least one intake unit with water.
In another representation, the issues described above may be addressed by a method for removing coking deposits from at least one injection nozzle of an Otto-cycle engine, by means of which at least one injection nozzle a fuel can be injected directly into a combustion chamber of the Otto-cycle engine, comprising temporarily humidifying intake air of the Otto cycle engine with water during operation of the Otto-cycle engine.
In yet another representation, the issues described above may be addressed by a method comprising humidifying intake air of an intake system of an engine in response to a determination that fuel injector coking is occurring, or after a duration has passed since a most recent humidification event.
In this way, by humidifying the intake air supplied to one or more combustion chambers of the engine system, coking deposits on one or more direct fuel injectors may be reduced. As such, fuel injection capabilities of the injectors may be increased, and a more accurate amount of fuel may be injected into the combustion chambers. Thus, emissions may be reduced, and an amount of power output by the engine system may be increased.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.